Measurements of absolute rate coefficients for the reactions of CN radicals with H2O, H2, and CO2 in the temperature range 295 K≤T≤1027 K

Abstract

Absolute rate coefficients were measured at different temperatures by means of laser photolysis-laser induced fluorescence technique for the reactions: CN+H2O→HCN+OH (1) CN+H2→HCN+H (2) CN+CO2→OCN+CO. (3) The temperature dependent rate coefficients for reactions (1) and (2) could be fit by Arrhenius expressions and are: k1(518−1027 K)=(8.0±0.8)×1012 exp [−(31.2±0.6) kJ/RT] cm3 mol−1 s−1k2(295−1000 K)=(2.1±0.2)×1013 exp [−(19.7±0.5) kJ/RT] cm3 mol−1 s−1. From thermodynamical properties of Rxn. (1) we evaluated the temperature dependent rate coefficient for the reverse reaction: k−1=(7.7±1)×1012 exp [−(34.6±1) kJ/RT] cm3 mol−1 s−1. In the CN+CO2 system we did not observe CN 1st order rate constants attributable to chemical reaction at temperatures up to 1000 K. We estimated an upper limit for k3 of 2.5×109 cm3 mol−1 s−1. The experimental results are compared with literature data. In the case of Rxn. (1) and (2) the agreement with previous experimental and theoretical studies is good, whereas our results for k3 are strongly different from former measurements.